The present invention relates to a wheel suspension system. More particularly, the present invention relates to a wheel suspension system which is characterized by a novel spring structure and a novel spring mounting arrangement, and a spring for such a wheel suspension system.
Conventionally, in a strut type wheel suspension system, for instance, which is widely used in automobiles, a vehicle body and a link member of the wheel suspension system are connected to each other by an assembly including a tubular shock absorber consisting of a cylinder filled with oil and a piston received therein, and a compression coil spring surrounding the shock absorber. However, because the input from the tire does not necessarily align with the axial line of the shock absorber, and the shock absorber is subjected to a lateral load, the sliding part between the cylinder and the piston of the shock absorber is subjected to a lateral force and a moment so that the resulting sliding resistance impairs the ride comfort of the vehicle, and the durability of the shock absorber is diminished.
In view of this problem, conventionally, it was known to provide an angular offset between the axial line of the spring and the axial line of the shock absorber so as to produce a force and a moment in the spring which oppose those produced in the sliding part between the cylinder and the piston of the shock absorber. However, the amount of offset is limited by the diameter of the coil spring and the mounting space, and it was not always possible to produce an adequate lateral force and moment to entirely cancel the lateral force and moment produced from the input to the tire.
In Japanese patent laid-open publication No. 01-156119, it is proposed to use a coil spring having a curved axial line in its free state so as to cancel the force and moment produced in the sliding part between the cylinder and the piston of the shock absorber. However, it is not clear how a curved coil spring may be retained in a straight state, and curved coil springs suitable for wheel suspension systems cannot be manufactured at low cost.
In view of such problems of the prior art, a primary object of the present invention is to provide a vehicle wheel suspension system comprising a tubular shock absorber, and a compression coil spring surrounding the shock absorber which can favorably reduce the sliding resistance that may be produced between the cylinder and the piston of the shock absorber without increasing the size of the system.
A second object of the present invention is to provide a vehicle wheel suspension system which can favorably reduce the sliding resistance that may be produced between the cylinder and the piston of the shock absorber, and can thereby improve the ride comfort of the vehicle and the durability of the shock absorber.
A third object of the present invention is to provide a vehicle wheel suspension system which can favorably reduce the sliding resistance that may be produced between the cylinder and the piston of the shock absorber without increasing the size of the system and without complicating the assembly work.
A fourth object of the present invention is to provide coil springs which are suitable for use in such vehicle wheel suspension systems.
According to the present invention, such objects can be accomplished by providing a vehicle wheel suspension system comprising a tubular shock absorber, and a compression coil spring surrounding the shock absorber, characterized by that: the compression coil spring is adapted to produce lateral forces between two ends thereof as the compression coil spring is extended and compressed.
In particular, when the lateral forces which are produced between the two ends are determined such that lateral forces which are produced between a piston and a cylinder of the shock absorber due to an offset between the line of action from a wheel and an axial line of the shock absorber may be minimized. Thus, the sliding resistance due to the lateral force acting between the cylinder and piston of the shock absorber can be favorably reduced so that the ride comfort of the vehicle and the durability of the shock absorber can be both improved.
The compression coil spring can be adapted to produce the required lateral forces between the two ends thereof as it is compressed and extended without increasing the size of the system and without suffering from geometrical restrictions if the compression coil spring consists of a coil spring which is wound around an oblique cylinder, and retained so as to have an upright axial line by applying a lateral initial load thereto, and to be extended and compressed along the upright axial line.
Similar objects can be accomplished if the compression coil spring consists of a coil spring which is wound around a true cylinder, and retained so as to have an oblique axial line by applying a lateral initial load thereto, and to be extended and compressed along the oblique axial line, or the compression coil spring consists of a coil spring which is wound around a true cylinder so as to have a cyclically varying pitch angle between a local minimum and a local maximum for each turn, and retained so as to be extended and compressed along the upright axial line.